Wa aleykum assalam wa rahmatullahi wa barakaatuh
This ayah came to my mind when I read this thread :
" إِنَّهُ مَنْ يَتَّقِ وَيَصْبِرْ فَإِنَّ اللَّهَ لَا يُضِيعُ أَجْرَ الْمُحْسِنِين"
"Indeed, he who fears Allah and is patient, then indeed, Allah does not allow to be lost the reward of those who do good" (surah Yusuf: 90)
I agree with brother muslim56. I have also never heard a sheikh saying you must know what the reward is. No doubt it is best to know what the reward is, for that may motivate a person to be persistent in doing the good deed, but I doubt that it's a requirement, Wallahu A3lam.